1. Field of the Invention
This invention relates to photographic cameras having automatic and manual ranges of focusing control.
2. Description of the Prior Art
Many methods for automatically focusing a still or movie camera by controlling the position of the objective lens system in accordance with the photo-electrically sensed distance from the camera to an object to be photographed have been proposed. The distance metering aspect of the autofocusing device may be operated in a through-the-lens metering mode (TTL), such as, for example, disclosed in U.S. Pat. No. 3,972,056. In that patent, the objective lens system is utilized as a part of the distance metering optical system so that a fraction of the light passing through the objective lens contributes to the detection of the condition of sharp focus. Another possibility for distance metering is in an outside-the-lens metering mode (OTL) disclosed, for example, in U.S. Pat. Nos. 3,836,772 and 3,838,275. There, a distance metering optical system is provided which is entirely independent of the objective lens system to effect an equivalent result.
While the camera employing the TTL type autofocusing device is, because of its use of light entering through the objective lens along the optical axis thereof in measuring the distance, capable of maintaining the accuracy of focusing control independently of the camera-to-object distance and, in a theoretical sense, of realizing the condition of best focus over the entire focusing range from infinity to an extreme close-up, the accuracy of the latter type autofocusing device is adversely affected by the parallax between the optical axes of the distance metering and photo-taking systems. This is because the focusing control error due to the parallax is greatly increased when in close-ups.
In the market, however, there is a strong demand for cameras capable of focusing down to extremely short distances with close-up effect. To meet this demand, particularly in the cinematographic camera, the photo-taking optical system is constructed in the form of a zoom lens provided with not only the commonly accepted zoom range but also a macro-zoom range in order to permit making closer close-ups. In providing focusing in these two zoom ranges, it has been a common practice to operate a changeover device. With the camera having the macrozoom range in combination with the OTL type autofocusing device, however, the motion picture photography can be made only in the ordinary zoom range where the parallax is negligible in measuring the camera-to-object distance. A camera having the function of making motion picture photography with high accuracy of focusing control in both the ordinary zoom and macro-zoom ranges is not known to date.